3,349 research outputs found
A laser gyroscope system to detect the Gravito-Magnetic effect on Earth
Large scale square ring laser gyros with a length of four meters on each side
are approaching a sensitivity of 1x10^-11 rad/s/sqrt(Hz). This is about the
regime required to measure the gravitomagnetic effect (Lense Thirring) of the
Earth. For an ensemble of linearly independent gyros each measurement signal
depends upon the orientation of each single axis gyro with respect to the
rotational axis of the Earth. Therefore at least 3 gyros are necessary to
reconstruct the complete angular orientation of the apparatus. In general, the
setup consists of several laser gyroscopes (we would prefer more than 3 for
sufficient redundancy), rigidly referenced to each other. Adding more gyros for
one plane of observation provides a cross-check against intra-system biases and
furthermore has the advantage of improving the signal to noise ratio by the
square root of the number of gyros. In this paper we analyze a system of two
pairs of identical gyros (twins) with a slightly different orientation with
respect to the Earth axis. The twin gyro configuration has several interesting
properties. The relative angle can be controlled and provides a useful null
measurement. A quadruple twin system could reach a 1% sensitivity after 3:2
years of data, provided each square ring has 6 m length on a side, the system
is shot noise limited and there is no source for 1/f- noise.Comment: 9 pages, 6 figures. 2010 Honourable mention of the Gravity Research
Foundation; to be published on J. Mod. Phys.
A 1.82 m^2 ring laser gyroscope for nano-rotational motion sensing
We present a fully active-controlled He-Ne ring laser gyroscope, operating in
square cavity 1.35 m in side. The apparatus is designed to provide a very low
mechanical and thermal drift of the ring cavity geometry and is conceived to be
operative in two different orientations of the laser plane, in order to detect
rotations around the vertical or the horizontal direction. Since June 2010 the
system is active inside the Virgo interferometer central area with the aim of
performing high sensitivity measurements of environmental rotational noise. So
far, continuous not attempted operation of the gyroscope has been longer than
30 days. The main characteristics of the laser, the active remote-controlled
stabilization systems and the data acquisition techniques are presented. An
off-line data processing, supported by a simple model of the sensor, is shown
to improve the effective long term stability. A rotational sensitivity at the
level of ten nanoradiants per squareroot of Hz below 1 Hz, very close to the
required specification for the improvement of the Virgo suspension control
system, is demonstrated for the configuration where the laser plane is
horizontal
Selfdual strings and loop space Nahm equations
We give two independent arguments why the classical membrane fields should be
loops. The first argument comes from how we may construct selfdual strings in
the M5 brane from a loop space version of the Nahm equations. The second
argument is that there appears to be no infinite set of finite-dimensional Lie
algebras (such as for any ) that satisfies the algebraic structure
of the membrane theory.Comment: 28 pages, various additional comment
Higher Structures in M-Theory
The key open problem of string theory remains its non-perturbative completion
to M-theory. A decisive hint to its inner workings comes from numerous
appearances of higher structures in the limits of M-theory that are already
understood, such as higher degree flux fields and their dualities, or the
higher algebraic structures governing closed string field theory. These are all
controlled by the higher homotopy theory of derived categories, generalised
cohomology theories, and -algebras. This is the introductory chapter
to the proceedings of the LMS/EPSRC Durham Symposium on Higher Structures in
M-Theory. We first review higher structures as well as their motivation in
string theory and beyond. Then we list the contributions in this volume,
putting them into context.Comment: 22 pages, Introductory Article to Proceedings of LMS/EPSRC Durham
Symposium Higher Structures in M-Theory, August 2018, references update
Optical spectra obtained from amorphous films of rubrene: Evidence for predominance of twisted isomer
In order to investigate the optical properties of rubrene we study the
vibronic progression of the first absorption band (lowest \pi -> \pi^*
transition). We analyze the dielectric function of rubrene in solution and thin
films using the displaced harmonic oscillator model and derive all relevant
parameters of the vibronic progression. The findings are supplemented by
density functional calculations using B3LYP hybrid functionals. Our theoretical
results for the molecule in two different conformations, i.e. with a twisted or
planar tetracene backbone, are in very good agreement with the experimental
data obtained for rubrene in solution and thin films. Moreover, a simulation
based on the monomer spectrum and the calculated transition energies of the two
conformations indicates that the thin film spectrum of rubrene is dominated by
the twisted isomer.Comment: 7 pages, 6 figure
Diffusion of electrons in two-dimensional disordered symplectic systems
Diffusion of electrons in two-dimensional disordered systems with spin-orbit
interactions is investigated numerically. Asymptotic behaviors of the second
moment of the wave packet and of the temporal auto-correlation function are
examined. At the critical point, the auto-correlation function exhibits the
power-law decay with a non-conventional exponent which is related to
the fractal structure in the energy spectrum and in the wave functions. In the
metallic regime, the present results imply that transport properties can be
described by the diffusion equation for normal metals.Comment: 4 pages RevTeX. Figures are available on request either via fax or
e-mail. To be published in Phys. Rev.
Energy-level statistics at the metal-insulator transition in anisotropic systems
We study the three-dimensional Anderson model of localization with
anisotropic hopping, i.e. weakly coupled chains and weakly coupled planes. In
our extensive numerical study we identify and characterize the metal-insulator
transition using energy-level statistics. The values of the critical disorder
are consistent with results of previous studies, including the
transfer-matrix method and multifractal analysis of the wave functions.
decreases from its isotropic value with a power law as a function of
anisotropy. Using high accuracy data for large system sizes we estimate the
critical exponent . This is in agreement with its value in the
isotropic case and in other models of the orthogonal universality class. The
critical level statistics which is independent of the system size at the
transition changes from its isotropic form towards the Poisson statistics with
increasing anisotropy.Comment: 22 pages, including 8 figures, revtex few typos corrected, added
journal referenc
Statistics of Wave Functions in Disordered Systems with Applications to Coulomb Blockade Peak Spacing
Despite considerable work on the energy-level and wavefunction statistics of
disordered quantum systems, numerical studies of those statistics relevant for
electron-electron interactions in mesoscopic systems have been lacking. We plug
this gap by using a tight-binding model to study a wide variety of statistics
for the two-dimensional, disordered quantum system in the diffusive regime. Our
results are in good agreement with random matrix theory (or its extensions) for
simple statistics such as the probability distribution of energy levels or
spatial correlation of a wavefunction. However, we see substantial disagreement
in several statistics which involve both integrating over space and different
energy levels, indicating that disordered systems are more complex than
previously thought. These are exactly the quantities relevant to
electron-electron interaction effects in quantum dots; in fact, we apply these
results to the Coulomb blockade, where we find altered spacings between
conductance peaks and wider spin distributions than traditionally expected.Comment: Accepted for publication in Phys Rev
- …